The present invention relates to a method of controlling the speed of a ship equipped with a controllable pitch propeller at a predetermined value.
As an example of the prior art methods for controlling the main engine and the controllable pitch propeller of controllable pitch propeller equipped ships, a method is known which is used with the automatic load control system generally abbreviated to ALC. The ALC system controls the blade angle of the controllable pitch propeller in such a manner that the hatched area in FIG. 1 becomes the operating region of the main engine. More specifically, the upper limit is defined by the main engine desired load characteristic designated at "a" in FIG. 1 and the lower limit is defined by the line "b" determined to provide a certain margin with respect to the characteristic "a", so that if the current operating condition goes beyond the upper limit (an overload condition) or the lower limit (a low load condition) due to the external conditions, the blade angle of the controllable pitch propeller is controlled so as to always maintain the operating condition within the hatched region.
Thus, there is a disadvantage that although the ALC system effectively utilizes the main engine output, no consideration is given to the propeller efficiency with the result that the optimum efficiency cannot be obtained and hence the minimum fuel consumption cannot be attained under the existing ship speed and external conditions.
Another method of maintaining the speed of a ship at a predetermined value is disclosed in the Japanese Laid-Open Patent Application Publication No. 52-22298 and this method does not clearly show the method of controlling the revolutions of the main engine.